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Spinal cord tuberculosis (TB) is a rare but potentially devastating manifestation of extrapulmonary tuberculosis that can lead to significant neurological impairment if not diagnosed and treated early. The condition is caused by Mycobacterium tuberculosis and typically presents as a granulomatous infection in the spinal cord, often involving the vertebral bodies, intervertebral discs, and epidural space. Spinal tuberculosis, or Pott’s disease, is primarily characterized by vertebral collapse, abscess formation, and cord compression. In some cases, however, the involvement of the spinal cord itself can occur without overt bony changes, making diagnosis challenging using traditional imaging techniques. Magnetic resonance imaging (MRI) is the gold standard for evaluating spinal pathologies, including spinal tuberculosis, as it provides detailed soft tissue contrast. Recently, diffusion-weighted imaging (DWI) has gained attention as a valuable MRI sequence for assessing spinal infections, including spinal cord tuberculosis. This article discusses the radiological features of spinal cord tuberculosis on DWI and conventional MRI, highlighting the advantages of these imaging modalities in early diagnosis and monitoring of the disease [1].

Pathophysiology of Spinal Cord Tuberculosis

Spinal cord tuberculosis can occur as a result of direct extension from a focus of infection in the vertebral body or through hematogenous spread. The infection usually starts in the vertebral bone, leading to vertebral osteomyelitis and discitis, and can subsequently extend to the epidural space. In some cases, the infection reaches the spinal cord itself, causing granulomatous inflammation and sometimes parenchymal damage. The resultant lesions may present as focal masses or diffuse involvement of the spinal cord, often accompanied by myelitis, abscess formation, and neurological deficits. The clinical presentation of spinal cord tuberculosis can vary depending on the level and extent of spinal involvement but often includes symptoms such as back pain, limb weakness, sensory deficits, and sphincter disturbances. Early detection and appropriate treatment are crucial for preventing permanent neurological damage and improving patient outcomes [2].

Conventional MRI Features of Spinal Cord Tuberculosis

Conventional MRI is the most commonly used imaging modality for diagnosing spinal cord tuberculosis. MRI provides detailed anatomic visualization of the spinal cord and surrounding structures, allowing for the identification of both osseous and soft tissue involvement. The hallmark features of spinal tuberculosis on MRI include:

Vertebral Involvement: MRI typically shows vertebral body destruction, which is seen as a decrease in vertebral signal intensity on T1-weighted images and an increase in signal intensity on T2-weighted images due to edema and infection. The intervertebral disc may appear collapsed or irregular, with potential loss of disc height.

Epidural and Paravertebral Abscesses: MRI may reveal epidural abscesses, which appear as areas of low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, often associated with compression of the spinal cord. Paravertebral soft tissue involvement may also be seen in the form of abscesses or granulomatous masses.

Spinal Cord Involvement: In cases of direct spinal cord involvement, MRI demonstrates abnormal areas of increased signal intensity in the cord, especially on T2-weighted images. These areas correspond to regions of inflammation, ischemia, and tissue destruction caused by the infection.

Caseous Necrosis: A characteristic feature of spinal tuberculosis is the presence of caseous necrosis, which can be seen as areas of central necrosis within the abscess or granulomatous tissue. These areas are often hypointense on T1-weighted images and hyperintense on T2-weighted images [3].

Diffusion-Weighted Imaging (DWI) in Spinal Cord Tuberculosis

Diffusion-weighted imaging (DWI) is an advanced MRI technique that assesses the movement of water molecules within tissues. It is based on the principle that the diffusion of water molecules is restricted in pathological tissues such as tumors and abscesses due to cellular density, making it particularly useful in the evaluation of infectious and inflammatory conditions. In spinal cord tuberculosis, DWI provides unique insights into the extent of infection and tissue changes that are not always apparent on conventional MRI [4].

Restricted Diffusion in Tuberculous Lesions: One of the most prominent features of spinal cord tuberculosis on DWI is the presence of restricted diffusion within the tuberculous granulomas or abscesses. These lesions typically appear as areas of high signal intensity on DWI, with corresponding low signal intensity on apparent diffusion coefficient (ADC) maps. Restricted diffusion is indicative of a high cellular content, which is often associated with active inflammation, pus, or granulomatous tissue.

Abscess Detection: DWI is particularly effective in identifying epidural and paravertebral abscesses associated with spinal tuberculosis. These abscesses typically show significant diffusion restriction, which helps distinguish them from other fluid collections or cystic lesions. The high signal intensity on DWI and low signal intensity on ADC maps correspond to the presence of pus, which has low water diffusion due to its high viscosity and cellular content.

Assessment of Spinal Cord Myelitis: In cases of spinal cord involvement, DWI can help assess the degree of myelitis (inflammation of the spinal cord), which is a common manifestation of spinal tuberculosis. Areas of myelitis may demonstrate mild to moderate restricted diffusion, indicating cellular inflammation. This feature is important in distinguishing between infectious and non-infectious causes of myelitis, such as multiple sclerosis or transverse myelitis [5].

Differentiating Active Infection from Chronic Changes: One of the major advantages of DWI in spinal cord tuberculosis is its ability to differentiate between active infection and chronic sequelae such as fibrosis or scar tissue. Chronic lesions, which may appear as areas of T2 hyperintensity on conventional MRI, often do not show restricted diffusion, whereas active tuberculosis lesions exhibit marked diffusion restriction. This distinction is crucial for monitoring treatment response and detecting relapse.

Clinical Significance of DWI and MRI in Spinal Cord Tuberculosis

The combination of conventional MRI and DWI provides a comprehensive approach to diagnosing and managing spinal cord tuberculosis. Conventional MRI allows for the detailed assessment of structural abnormalities, including vertebral destruction, abscess formation, and spinal cord involvement. DWI, on the other hand, provides functional insights into the metabolic activity of the lesions, helping to identify areas of active infection and differentiate them from non-infectious or post-treatment changes. The ability to detect early lesions, evaluate the extent of the disease, and monitor treatment response is critical in managing spinal tuberculosis. DWI, in particular, is invaluable for identifying areas of active infection and guiding biopsy or surgical intervention when necessary. Additionally, DWI can be used to assess treatment efficacy by monitoring changes in the diffusion characteristics of the lesions over time, which can help inform decisions regarding the duration of antimicrobial therapy [6].

Limitations and Future Directions

While DWI offers significant advantages in the evaluation of spinal cord tuberculosis, it is not without limitations. DWI is highly sensitive to motion artifacts, which can make imaging difficult in patients with severe pain or limited mobility. Additionally, the interpretation of DWI in the spinal cord can be challenging due to the complex anatomy and potential for overlapping signal intensities with other conditions, such as tumors or multiple sclerosis. Future research should focus on refining DWI techniques to improve spatial resolution and reduce motion artifacts, as well as developing advanced algorithms for automated image analysis to enhance diagnostic accuracy. Further studies are also needed to establish standardized DWI criteria for the evaluation of spinal cord tuberculosis and to investigate its role in monitoring treatment response and predicting clinical outcomes [7].

Conclusion

Diffusion-weighted imaging (DWI) represents a valuable tool in the radiological assessment of spinal cord tuberculosis, providing critical information about the cellular characteristics of infected tissues that may not be apparent on conventional MRI. By offering high sensitivity for detecting active infection, abscess formation, and myelitis, DWI enhances the ability to diagnose spinal tuberculosis early and accurately. When combined with conventional MRI, DWI improves the overall sensitivity and specificity of spinal tuberculosis detection, helping guide appropriate management and optimize patient outcomes. Further advancements in imaging technology and research will continue to refine the role of DWI in spinal cord tuberculosis and other spinal infections.

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